New method for the evaluation of the response of cultured cell lines to continuous low-dose-rate irradiation from encapsulated iridium-192 seeds with hyperthermia

A new method was designed to investigate and evaluate the biological effectiveness of hyperthermia combined with continuous low-dose-rate irradiation (CLDRI) from encapsulated iridium-192 seed sources on glioma cells in vitro using the MTT assay. The system consists of 10 iridium seeds contained in a catheter bent into a circle, which is placed on a culture plate containing the cells. The effects of CLDRI and CLDRI combined with hyperthermia on a cultured rat glioma call line (C-6) were studied. The number of surviving cells decreased as the total radiation dose increased. There was no significant difference in survival rates at dose rates of 0.1 Gy/hr and of 0.2 Gy/hr (p=0.2811). An additive effect was observed in the cells treated with hyperthermia at 41degC and 42degC, combined with CLDRI, and a synergistic effect between the two treatment modalities was observed at 43degC. This new device is less expensive, easily reproducible, and can also be performed easily enough to examine a large number of samples in a short time period for sensitivity testing. (author)